CtBP (carboxyl-terminal binding protein) was initially identified through its ability to interact with a motif in the carboxyl-terminus of the adenoviral transforming protein, E1A. In many ways, the functions of CtBP exactly oppose those of the better-characterized E1A binding transcriptional co-activators, CBP and p300. While CBP and p300 have been extensively studied, the functions of CtBP have been relatively unexplored. This proposal describes experiments that should increase the appreciation of CtBP as a transcriptional co-regulator and adapter protein. The first aim is to determine the functional importance of interactions between CtBP and transcriptional regulators identified in a yeast two-hybrid screen. These studies will address, in particular, Teashirt, MyT1, Prox-1, RING3, and RIZ, proteins believed to e important for transcriptional repression and cell cycle regulation during development. Additional components of CTBP complexes will be identified in mass spectrometry. The second aim will be to test the hypothesis that nicotinamide adenine dinucleotide-induced alternations in CtBP structure allow the activities of selected transcriptional repressors to sense cellular redox state and hence, to monitor cellular energy levels. These studies are based on the finding that NAD and NADH dramatically stimulate the interaction of CtBP with its prototypical binding protein, E1A. If this mechanism can be generalized, it would imply that certain developmentally important transcriptional pathways could be regulated by nutrition and other factors that influence cellular metabolism. The third aim is to develop how an amino- terminally extended form of CtBP, termed Ribeye, contributes the unique functional properties of the ribbon synapse. These studies will use capacitance recordings and evanescent field microscopy to ask whether agents that modulate CtBP binding properties affect specific aspects of secretion in bipolar neurons.